An arrangement in which, when a subject vehicle is passing a parking space, the relative distance from the subject vehicle to surrounding objects is detected by means of a distance sensor formed from a laser radar or a photosensor, the position of the subject vehicle is detected by means of a steering angle sensor and a vehicle speed sensor, prestored subject vehicle external dimensions or minimum turning radius-related information is compared with the detection results from the above sensors to thus determine whether or not there is a space that can be parked in or the parking space can be parked in when moving with the minimum turning radius, and the driver is informed of this by voice is known from Patent Document 1 below.
In the same way as in Patent Document 1 above, an arrangement in which, when a subject vehicle is passing a parking space, the existence of a parking space is determined by detecting the state of obstacles is known from Patent Documents 2 and 3 below.    [Patent Document 1] Japanese Patent Application Laid-open No. 9-180100    [Patent Document 2] Japanese Patent Application Laid-open No. 2002-154396    [Patent Document 3] Japanese Patent Application Laid-open No. 2002-243857